Heretofore, polyamide resins such as polyamide 11, polyamide 12 and the like are used in wide-range applications because of high chemical resistance thereof, and are, for example, widely used for various structures such as pipes, hoses, tubes, etc. Recently, from the viewpoint of prevention of environmental pollution, rigorous exhaust restrictions have been applied, and for example, the above-mentioned various structures for use for fuel oil have become desired to have high barrier properties for the purpose of preventing volatile components such as volatile hydrocarbons and the like from penetrating through the structures to be diffused out in air.
However, various structures formed of polyamide resins, especially polyamide 11 or polyamide 12 excellent in strength, toughness, chemical resistance and flexibility could not have sufficient barrier properties against volatile hydrocarbons and the like, and improvement thereof is desired. In addition, recently, an alcohol gasoline containing an alcohol such as methanol, ethanol or the like blended therein has been being put into practical use, but alcohol gasoline has high permeability and readily vaporizes in air, and therefore the barrier properties thereof need to be increased more.
As a means for enhancing the barrier properties, proposed is a multilayer structure that is provided with a barrier layer excellent in barrier properties in addition to a polyamide layer composed of polyamide 11 or polyamide 12.
For example, PTL 1 discloses a multilayer structure containing a polyamide layer composed of polyamide 11 and/or polyamide 12 and a barrier layer composed of polyamide 9T.
In addition, for example, PTL 2 describes a laminate having a thermoplastic resin composition layer containing different kinds of polyamide resins and a carbodiimide compound, and a polyamide resin layer composed of polyamide 11 and/or polyamide 12.
Further, for example, PTL 3 describes a tube having a barrier layer that contains a metaxylylene group-containing polyamide resin and a specific amount of a flexible resin miscible with the metaxylylene group-containing polyamide resin.